Defiant
I haven't heard the 219ia so I can't offer a personal opinion between the 2 but from reading it would seem that the 219ia has a little more refinement. From my vantage point the 518ia is a quality made product, I have had zero issues with it.
Specific to the 518ia - here's the link to Herb Reichert's Stereophile Review of the 518IA - you may want to read it in its entirety -
https://www.stereophile.com/content/line-magnetic-audio-lm-518ia-integrated-amplifier - but here's an excerpt from his conclusion "
But now, under full review-level scrutiny, I at last recognized the LM-518IA's complete array of virtues. It is musically alive and vigorous. It moves forward like a caffeinated child chasing a scared cat. It is strong. It has easily driven every speaker I have tried with it. It plays music with rare charm and sensitivity. Its beguiling light illuminates one of the most detailed soundstages I have ever heard as a reviewer. It is reliable: I have used and abused this 77-lb machine for more than a year and, more than any other amp I have reviewed, it seems indestructible.
Here are links to 2 other reviews
http://wallofsound.ca/audioreviews/line-magnetic-518ia-integrated-amplifier/https://witchdoctor.co.nz/index.php/2014/06/line-magnetic-lm-518ia-integrated-set-amplifier-review/In the witchdoctor review he claims that he had some transformer hum; I can honestly state that I have not heard any in the almost 2 years that I have had the amp